Surfaces and interfaces with and without chemical and physical conditioning such as, for example, defect, impurity, adsorption, passivation, alloy and compound formation, have been a key driver in physics, chemistry, and materials sciences. Collecting meaningful information about the dynamics and energetics of bonds and electrons in a selected region at the atomic-scale is important to the understanding what is and will be happening in the specific region. This assists researchers in designing processes and materials to achieve desired functions.
The energetics and dynamics of interatomic bonding and electronic distribution in both real and energy spaces dictate the performance of a material and a functional device. Defects, surface characteristics, impurities, and interfaces are key components of materials interacting with the environment for function realization such as, for example, growth nucleation and catalytic reaction, etc. It has long been a challenge to gaining information, in particular, at the atomic scale in a specifically selected site about the statics (order, nature, length, strength) and the dynamics (formation, dissociation, relaxation and vibration) of bond forming and the associated energetics and kinetics of electron transportation, polarization, localization and densification under varied conditions has long been a challenge. Understanding and grasping with factors controlling the bonding and electronic process has been the pursuit of several generations of the scientific community and such information is of paramount importance.
By using a scanning tunneling microscopy/spectroscopy (STM/S) it is possible to obtain an image of an individual atom by probing the flow of charge with energies near the Fermi level under bias crossing the tip and the sample surface of conductors or semiconductors as exampled in FIG. 1. The STM mapped graphite surface and the STS probed energy states of the graphite surface with and without a defect vacancy show that the vacancy exhibits protrusions and Fermi resonant states or Dirac fermions. However, the physical origin is unclear. As such the information obtained is limited only to the top edge of the valence band in energy space and to the top side of the specific surface atom in real space. Therefore, it is difficult to collect information about the bonds and electrons limited to the specific zones of atomic-scaled dimension and electrons with energies beyond the scope of STM/S. Hence, it is hard to determine what is happening to the bonds between the atoms being investigated and those underneath; and what is happening to the local electrons in the valence band and below by using STM/S alone.
Generally, the ES collects information from several nanometers in depth of electrons with energy in the valence band and below, which is determined by the interatomic bonding interaction.
FIG. 2 compares the raw XPS data for (a) Rh and (b) Pt homogeneously adsorbed adatoms. Traditionally, optoelectronic spectra are analysed by decomposition of the spectra into several components. From the conventional ES data decomposition, it is difficult to gain information of the contribution from the surface before and after physical and chemical conditioning as the signal due to modification is rather weak. Also, uncertainty remains regarding the number and energies of the components in the raw ES data decomposition.
Therefore, gaining atomic-scaled, firmly-defined information of bonds and electrons in the selected zones beyond that which an STM/S can scope, and in the energy window below that which an STM/S can probe, is desirable for materials design and processes control. The selected zones may be in the surface, subsurface, surrounding defect or impurity or bulk interior at the atomic scale within the depth scope of electronic spectroscopy up to several nanometers.